A contactless power transfer apparatus uses electromagnetic induction between a primary coil (power transmission coil) and a secondary coil (power reception coil) to supply power from the power transmission coil to the power reception coil. The contactless power transfer apparatus is expected to be widely spread as a rower transfer apparatus which charges a secondary battery mounted to an electric vehicle or a plug-in hybrid vehicle.
FIG. 37 illustrates a power transfer system of a plug-in hybrid vehicle which uses the contactless power transfer apparatus. A vehicle with an engine 154 and a motor 153 mounted as driving sources includes a secondary battery 151 which is a power supply for the motor 153, an inverter 152 which converts a direct current of the secondary battery 151 into an alternating current to supply the alternating current to the motor 153, a power reception coil 133 of the contactless power transfer apparatus, a rectifier 140 which converts the alternating current received by the power reception coil 133 into the direct current to supply the direct current to the secondary battery 151, and a capacitor 134 which is connected between the power reception coil 133 and the rectifier 140 in parallel. The power reception coil 133 is provided outside a floor of a vehicle body.
In the meantime, a power transfer station side (on the ground) includes an alternating current power supply having a commercial frequency, a rectifier 110 which converts the alternating current into a direct current, an inverter 120 which generates a high frequency alternating current from the direct current, and a power transmission coil 131 of the contactless power transfer apparatus. A driver stops the vehicle at a position where the power reception coil 133 is disposed directly on the power transmission coil 131 to start feeding power to the secondary battery 151.
In the power transfer system, even when the position of the power reception coil 133 is deviated with respect to the power transmission coil 131 or a gap between the coils is increased, a wide opposing area between coils needs to be established so as not to lower a power reception efficiency.
As a coil of a contactless power transfer apparatus for a vehicle, a coil (a single-sided winding coil) which is arranged by winding an electric wire in a spiral form in a single side of a flat ferrite core and a coil (double-sided winding coil) which winds an electric wire around the core are known. However, regarding the misalignment between coils, the double-sided winding coil has a smaller size than the single-sided winding coil so as to have advantages for good tolerance to the misalignment between coils and the small size of the power reception coil may be achieved by the double-sided winding coil.
In the following Patent Literature 1, the present inventors suggest that a coil 164 is wound around an H-shaped ferrite core 160 illustrated in FIG. 38 to form a power transmission coil and a power reception coil of the contactless power transfer system. FIGS. 38A to 38C illustrates a state in which the coil 164 is wound around the core 160 and FIGS. 38D to 38F illustrates a state in which only the core 160 exists.
In the case of the H-shaped core 160, the coil 164 is wound around a horizontal bar portion 163 of a letter H and vertical parallel bar portions 161 and 162 serve as magnetic poles into which magnetic flux enter or from which magnetic flux exit. As illustrated in FIG. 39, a main magnetic flux 190 which is output from the magnetic pole portion of the H-shaped core of a power transmission coil 170 enters the magnetic pole portion of the H-shaped core of a power reception coil 180. In a horizontal bar portion 181 around which a coil 182 is wound, the main magnetic flux proceeds in the core, is output from the other magnetic pole portion, and enters the magnetic pole portion of the H-shaped core of the power transmission coil 170.
A spatial magnetic flux distribution between a primary side core and a secondary side core is determined by shapes of the magnetic pole portions 161 and 162, and a magnetomotive force of the coil is determined by (an amount of a coil current)×(a number of windings). Therefore, if the shapes of the magnetic pole portions 161 and 162 and the number of windings of the coil 164 are changed, even though a width of the horizontal portion 163 of a letter H is narrowed to reduce a usage amount of the ferrite, the magnetomotive force of the core is not changed. In the meantime, a coil length (that is, an entire length of the electric wire) is (a length of an outer periphery of the horizontal bar portion of H)×(the number of winding) so that if the width of the horizontal bar portion of H is narrowed, the coil length is also reduced, a resistance of the coil is reduced, and a weight of the coil is lowered.
In the contactless power transfer apparatus which uses the double-sided winding coil, a core member which covers a non-opposite-face side of the coil like the single-sided wounding coil is not provided so that, as illustrated in FIG. 39, leakage magnetic fluxes 191 and 192 which detour the non-opposite-face side of the coil are generated. If the leakage magnetic flux 192 permeates a steel plate of the floor of the vehicle body, an induced current flows therein to heat the steel plate so that power transfer efficiency is significantly lowered. Therefore, in the contactless power transfer apparatus which uses the double-sided winding coil, it is required to arrange a non-magnetic good conductor (non-magnetic conductor plate) such as an aluminum plate 173 or 183 on the rear surface of the coil to perform magnetic screening of the leakage magnetic fluxes 191 and 192.
An area of the non-magnetic conductor plate 183 which is provided on the rear surface of the power reception coil 180 is desirably set to have a size enough to arrange substantially entire power transmission coil 170 below the non-magnetic conductor plate 183 even when the power reception coil 180 is arranged in anywhere within an tolerable range of the misalignment. Therefore, the area of the non-magnetic conductor plate 183 is much larger than an area of a plane shape of the power reception coil 180.